This invention relates generally to diagnostic ultrasound medical imaging, and more particularly, to methods and apparatus for detecting nonlinear echoes from contrast agents.
Contrast agents can be used in diagnostic medical imaging to aid in the detection of diseased tissues. In some detection methods, the nonlinear response of the contrast agent relative to normal tissue is used to distinguish between ultrasound echoes resulting from the presence of contrast agent from those of normal tissue.
Ultrasound contrast imaging methods are known that use multiple pulses where at least two pulses are of different amplitude and at least two pulses are of different phases. The multiple pulse techniques suppress the linear echo and preserve the nonlinear echoes from contrast agents. These techniques, however, work well only when the transmit pulses that have a 180 degree phase shift with respect to each other are exactly symmetric (i.e., the sum of the pulses with 180 degree phase shift with respect to each other is zero).